Understanding Fermentation Temperature Control

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By Kara Taylor, White Labs

When I started homebrewing in college, I never really thought about controlling my fermentation temperature. For one, it was an extra step in the day-long brewing process, and two, it typically required an investment I didn’t own on my college budget. 

Little did I know that controlling the temperature of my fermentations was hands down the best investment I could have made in the quality of my homebrew. If you’re like I was, finding that your homebrew has some off flavors that you can’t quite pinpoint, you’d likely benefit from understanding how to dial in your temperature control.

Beer styles determine fermentation temperature

Fermentation temperature is the main difference between creating ale and lager styles. While we typically attribute this to the type of yeast strain, as we’ve learned more about yeast genetics, many traditional lagers strains are actually genetically ale strains and vice versa. Therefore, fermentation temperatures can be played around with a variety of strains. The temperature of yeast-driven styles, like saison or hefeweizen, is critical in the stylistic accuracy of the beer.

What happens when I raise or lower the fermentation temperature? 

Brewer’s yeast is typically very happy growing at 80-90℉ (86-32℃). They will multiply quickly, and propagation at a yeast lab at this temperature is not uncommon. But most fermentations at this temperature–depending on the strain–result in flavors that are typically undesirable. Suppose I used a traditionally “clean” strain, such as WLP090 San Diego Super Yeast, and fermented this strain with no temperature control in July versus December. In that case, I’d have a very different outcome. 

Generally speaking, fermentation byproducts like esters and fusels increase as temperature rises. As the fermentation temperature decreases, we see lower expressions of flavor and aroma. Sometimes an increase in aroma can be pleasant, such as with a saison-style beer. When it’s fermented at a lower temperature, the floral, fruity, spicy character of the saison is lower. When that saison is allowed to ferment higher or at room temperatures, we see a fruity, floral, bubblegum aroma.

On the contrary, a different yeast strain, such as the English ale yeast, the ester profile could become solvent-y like nail polish. It could be described as “hot” and create a burning sensation. Because of these off-flavors, most brewer’s yeast has a sweet spot where the most optimal flavors and aromas are produced. 

To understand fermentation temperature control, we must also understand the role of enzymes in fermentation. Enzymes are present in many parts of the brewing process (i.e., malting barley) and are responsible for the flavor, aroma, and alcohol compounds produced from yeast. In the fermentation process, yeast contains intracellular enzymes that convert one substrate into another. For yeast to convert sugar to carbon dioxide and alcohol, many enzymes located inside the cell are involved. When the temperature increases, these enzymes are sped up. This is why, when we ferment warmer, the final gravity is reached faster than if the temperature was lower. When we cold ferment a lager, the enzymatic activity of the yeast is very slow and therefore takes weeks to ferment a proper lager. This isn’t because the yeast strain itself is slow- we are using temperature to control the fermentation speed. 

When it comes to other fermentation byproducts, the mechanism in which brewers yeast produces esters, fusels, phenols, and aldehydes is the same. It is through enzymatic pathways within the yeast cell. The difference between yeast strains is how enzymatically active these yeast perform. This is why fermenting at the suggested temperature range for many strains can be so important. 

Why does Kveik yeast break all of the rules?

Kveik yeast are the perfect strains of brewer’s yeast if you struggle with temperature control in your homebrewing. These yeast strains, originating from Norway, have a long history of fermenting in very warm temperatures with very few off flavors. They are considered “clean” yeast strains, free of phenolic compounds, and can be used in various styles. These strains make off-flavor-free beer when fermented at very high temperatures (>90℉). This is likely because of how brewers made beer in Norway at the time and selected yeast that made delicious beer. This is done by using the yeast from the best batch and reusing it again in the next. As this is done over and over for hundreds of years, it results in a yeast strain that ferments well in warm temperatures with little to no off-flavors. 

Additionally, these strains are known to be “super fermenters,” or yeast that can ferment very quickly. This is only the case because of the high fermentation temperature. Because of the fermentation temperature, the enzymatic activity of the yeast cell is higher and therefore consumes sugar quicker than your average brewer’s yeast. If these yeast strains were fermented at 68℉ (20℃) we would see average fermentation times for these yeast strains.

What can I do at home to help my fermentations?

If you’re not looking to invest in ways to control fermentation at home, the first step is to pick the right yeast strain. Many strains are more forgiving, such as Belgian, saison, or hefeweizen yeast. If you haven’t tried out a Kviek strain, this summer is the perfect time to do so. Additionally, find an area of your home that is more consistent in temperature, such as a closet. Investing in chest coolers or refrigeration is the next step and can be done relatively inexpensively with some DIY engineering. 

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About the Author

Kara Taylor has been with White Labs since 2009. She became interested in fermentation science while homebrewing during her days at Loyola Marymount University. She received a B.S. in biology in 2009 and began employment at White Labs in San Diego as a yeast laboratory technician. Since June 2021, she functions as the Head of Operations. She enjoys traveling the world judging beer and educating brewers about fermentation.

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